This invention relates generally to rotary valves and more particularly to such valves which are subjected to axial pressures resulting in axial thrust loads on the rotary spool.
While rotary valves have been widely used in hydraulics for some time, it has been recognized that the axial thrust loads often imposed upon the rotary spool requires a relatively high torque in order to rotate the spool. Since such valves are frequently used to meter fluid flow, a high torque level is undesirable. First, because the coefficient of static friction is higher than the coefficient of sliding friction, it is difficult to make relatively small control movements with the precision necessary to achieve the desired changes in flow rate. Second, the moment arm required to provide the needed rotational torque complicates the control mechanism therefor because excessive travel is often required. And finally, the use of push-pull or Bowden cables as a control means frequently places an upper limit on the force that can be transmitted to the movement arm. It is, therefore, apparent that a rotary valve structure which requires a low rotational torque to turn the rotary spool in such a valve is highly desirable.
Since rotary valves are frequently used in a valve body with plural pressure supply ports or in plural valve bodies having pressure supply ports located at different levels therein, it is often necessary to design the sleeve so that it is complementary to each of the rotary valve spools, which increases the cost of manufacture as well as multiplying the number of stock parts nad complicating servicing of the valves.
It is, therefore, an object of this invention to provide a rotary valve in which the rotational torque required to adjsut its angular position is low.
It is also an object of this invention to provide a rotary valve which can readily be adjusted or positioned solely through force transmitted by push-pull or Bowden cables.
It is a further object of this invention to provide a rotary valve in which the axial force creating the frictional force resisting rotation thereof is minimized.
It is a still further object of this invention to provide a rotary valve for use in a plurality of valve bodies with components which are common, which are less expensive to manufacture and which deminishes the number of stock components.